Phototherapy has been accepted since the early 1970s as a benign and effective means of treating hyperbilirubinemia of the newborn, but the long-term effects of the modality are as or yet unknown. The purpose of this study is to determine whether children who received phototherapy in infancy are at a higher risk of developing cancer. The study population is based on all children younger than 10 years of age who developed a malignancy in Israel between 1973 and 1984. Cases will be selected through the Israel National Cancer Registry. There will be two controls for each case comprised of children with the closest identity numbers matched by sex, birth weight and hospital of birth. Nursery records for the entire study population will be reviewed in detail. Full data regarding phototherapy and the duration of therapy will be abstracted, and the frequency of its use in cases and controls compared. The birth weight, sex, type of tumor (in selected categories), level and cause of hyperbilirubinemia and age at commencement of treatment will also be investigated as possible contributing factors.